1. Technical Field
The present invention relates to a private exchange system, and more particularly, to an integrated time switching and conference calling apparatus for performing time switching and conference calling functions.
2. Background Art
Private branch exchange (PBX) systems are well known for providing switched communications between a plurality of PBX subscriber telephones, computers, etc. The switched communications take place through a switching matrix where the actual signal interconnects between the PBX signal ports and at which the subscriber equipments such as telephones and computers are connected. In modern digital PBX systems, the signal information such as voice and data is typically in a byte wide, pulse code modulated (PCM) format, and the switching matrix is a time slot interchange (TSI) which time division multiplexes the PCM sample bytes between ports. Exemplars of contemporary practice in typical time division switching systems are disclosed in U.S. Pat. No. 4,430,733 for Switching Of Digital Signals issued to Hardy et al., U.S. Pat. No. 4,564,936 for Time Division Switching Network issued to Takahashi, U.S. Pat. No. 4,809,261 for Space And Time Switch For 22 PCM Highways issued to Radcliff, U.S. Pat. No. 4,841,522 for Time Division Channel Switching Circuit issued to Yamazaki, U.S. Pat. No. 4,858,227 for Space And Time Having Multiplexed Memories issued to Ratcliff, and U.S. Pat. No. 5,123,012 for Time Division Switching Apparatus issued to Suzuki et al.
Conference service may be included in the digital PBX systems to establish conference connections between subscribers with or without restriction as to the number of subscribers that may participate in a conference session. Conventional PBX systems which contain conference calling functions are disclosed, for example, in U.S. Pat. No. 4,119,807 for Digital Time Division Multiplexed Switching System issued to Nahay, U.S. Pat. No. 4,481,624 for Linear Time Division Multiplexed Conferencer issued to Baranyai et al., U.S. Pat. No. 4,509,166 for PCM Communication System And Method Of Operation issued to Simon, and U.S. Pat. No. 4,521,879 for Digital Private Branch Exchange issued to Gueldenpfennig et al. Generally, a conference calling unit is included in the digital PBX system to make available a range of conference sizes. In the contemporary conference service available in the digital PBX system, however, a central processing unit (CPU) is required to control time switching and conference calling functions separately via an interface circuit. Moreover, I have found that the incoming highways which are important factors for determining a number of allowed subscribers using the conference service are not allocated to the subscribers but are used only as system resources i.e., conference calling function.